People go through their lives making a series of "when" decisions based on gut instinct. This book says there's a better way. Moreover, it says that "when" often is more important or impactful than "what" or "how".
Not all times of the day are created equal. Energy, focus, physical readiness, and mental acuity ebb and flow through the day, following predictable patterns. For the majority of the population, we begin the day strong, then have a slump around 6-8 hours after we wake up, then end the day strong.
This bears out in a multitude of ways:
Scary real-world case-in-point: there are significant effects of the mid-afternoon slump in hospitals everywhere. You're 3x more likely to be killed by your anestesia. Staff are 10% less likely to have washed their hands, causing infection rates to rise. Colonoscopies find fewer cancerous growths.
Your chronotype determines is where the peak/trough take place in the day. The chronotypes follow a left-skewed normal distribution. Roughly, 30% are early birds, 50% are "third birds", and 20% are night-owls. The measuring method is to find the midpoint of your average night's sleep. Early birds have a midpoint before 4am. Night owls have a midpoint after 6am. Most people fall in-between. Midpoints tend to be earlier in early and late life, and much later around the teenage, early 20's years.
The negative effects of our standard energy pattern are not necessarily inevitable. The positive effects of a break are overlooked and under-appreciated.
Breaks can be of various types. There are vigilance breaks, in which you force yourself to stop and refer to a Standard Operating Procedure or checklist, or regular breaks.
5 Principles of breaks.